To prevent radiation from being released from a nuclear facility, an air-conditioning and ventilating apparatus is provided in the nuclear facility to remove radioactive iodine contained in gas. An iodine filter is provided in a chamber or the like in the air-conditioning and ventilating apparatus, and the iodine filter is accommodated in a casing in multiple stages and installed in the chamber or the like. As the iodine filter, an activated carbon filter having high removal efficiency of radioactive iodine has been conventionally used.
Generally, in such an iodine filter, removal efficiency of radioactive iodine by an activated carbon filled in the iodine filter is obtained, and a leak rate is measured in order to confirm the presence of a leakage from a minute gap, which may be generated between the iodine filter fitted in the chamber or the like and a gasket in the air-conditioning and ventilating apparatus.
When a minute gap is generated between the iodine filter and the gasket, a part of gas entering from an inlet side of the iodine filter does not pass through the iodine filter but passes through the minute gap and flows to a downstream side of the iodine filter. While passing through the gap, any gas is not collected. Therefore, an amount of gas passing though the gap and moving to the downstream side of the iodine filter depends on the size of the gap, regardless of the kind of substance of the gas.
A method of testing a leakage in the iodine filter includes a method of introducing Freon-112 (Chlorofluorocarbon R-112) into the iodine filter, and testing a concentration of Chlorofluorocarbon R-112 on an inlet side and an outlet side of the iodine filter by a gas chromatograph attached with an electron capture detector or the like, and a method of introducing non-radioactive methyl iodide into the iodine filter and testing a concentration of methyl iodide in the same manner as described above. Besides, there has been also proposed a method of introducing heavy water vapor into an iodine filter to detect a leakage (see, for example, Patent Literature 1).